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Silicon Chip ULD Mk3 amp - 0.0006% distortion
Silicon Chip ULD Mk3 amp - 0.0006% distortion
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Old 30th June 2011, 08:07 AM   #21
VHF man is offline VHF man  Australia
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Quote:
Originally Posted by wahab View Post
It had several non solved issues, dont know to what extent these
were solved in the current version..

There was an errata included with MK2 kits sold through local retailers Altronics and Jaycar after the fault was identified. 22K is actually a bit overkill. Iíve had no problems with 10K (bypassed with 10n) and I also substitute the bc639 with a 2SA2240 (lower cob and higher beta works best there). I did find that a small amount of VAS degeneration (22 ohms) was needed for unconditional stability.

There have been some smoked modules but mostly because people will fiddle with them 'live' and do not realise that the suppied generic 5A rail fuses will blow well after the output devices have internally melted down - like a Fukashima reactor.
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Old 3rd July 2011, 05:51 AM   #22
PHEONIX is offline PHEONIX  Australia
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Originally Posted by ostripper View Post
Is this amp 6 ppm THD20 ? At what output ? 6ppm is not hard to achieve these days. But can it "hold" that @ 100v p-p 20Khz ? 4R , anyone ? . If it's not a triple , highly doubtful ....
It does look like a nice build. Sporting those T-traks and using a real Vbe + 2 of the internal diodes must make for near perfect thermal response. Still , it is what it is.
PS - I can now beat TMC ... without TMC ( 2 designs).
OS
Hello Outstripper

The real amp does 0.004% THD @20Khz at 100watts into 8R less at 4R.

this is achieved with double EF ouput and not a tripple. Please note the ouput consists of a total of 4 output BJT devices.

Regards
Arthur
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Old 20th July 2011, 09:02 PM   #23
Oliphant is offline Oliphant  New Zealand
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Silicon Chip ULD Mk3 amp - 0.0006% distortion
I bought the mag yesterday & I can't help but wonder, why have they specified a 47uF bipolar input capacitor in the hp filter along with a 12k resistor? This would give a -3dB pt of .282Hz.... Surely this is a mistake and that they had meant this to be a 4.7uF cap giving a -3dB pt of 2.82Hz
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Old 20th July 2011, 09:57 PM   #24
jcx is offline jcx  United States
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"super sizing" electrolytic DC blocking caps has some justification - read
Self

basically if there's less V drop due to a bigger Cap's low Z then there's less "room" for distortion - Self shows AP distortion measurements in later editions of his amplifier book
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Old 21st July 2011, 12:17 AM   #25
Oliphant is offline Oliphant  New Zealand
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Silicon Chip ULD Mk3 amp - 0.0006% distortion
Thanks jcx. I might just try this with my next design and measure the difference between large and small input caps. I've recently recieved his latest edition of the power amplifier design handbook and I'll make sure to look this up
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Old 21st July 2011, 07:44 AM   #26
dchisholm is offline dchisholm  United States
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Are there any U.S. chains that carry "Silicon Chip" in paper? I used to get "Wireless World" at The Library, Limited - and I think they also had Silicon Chip - but when Border's came to St Louis, they died.

Dale
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Old 21st July 2011, 11:57 AM   #27
quadtech is offline quadtech  India
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Ironically, it's Borders turn to die now.
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Old 21st July 2011, 12:14 PM   #28
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Oliphant View Post
why have they specified a 47uF bipolar input capacitor in the hp filter along with a 12k resistor? This would give a -3dB pt of .282Hz.... Surely this is a mistake and that they had meant this to be a 4.7uF cap giving a -3dB pt of 2.82Hz
Quote:
Originally Posted by jcx View Post
"super sizing" electrolytic DC blocking caps has some justification - read
Self

basically if there's less V drop due to a bigger Cap's low Z then there's less "room" for distortion
a sensible 100ms filter can be achieved with low Rin and electrolytic or with medium Rin and large film or with high Rin and smaller film.
I favour film and adopt generally between 1uF and 4u7F allowing a range of Rin from a low of 20k to a high of 100k.

There seems to be no reason for adopting a large (or very large) electrolytic.
Well, there is a reason - electro is cheap !

At the NFB loop the DC blocker has to be electro to avoid the compromises that JLH adopted to allow a pair of film caps to be used.
If electro is adopted for the NFB DC blocker then it must be oversized such that the input filter determines the low frequency roll off.
If the NFB DC blocker is used to roll off the bass response then that guarantees that some AC voltage will be developed across the DC blocker.
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Last edited by AndrewT; 21st July 2011 at 12:17 PM.
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Old 1st February 2012, 01:59 AM   #29
farmerjack61 is offline farmerjack61  Australia
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Quote:
Originally Posted by Circlotron View Post
July 2011 SC mag.
Hello from Tassie.


I just wanted to share some info with those of us building this amp. It's all good!


In a way I am giving Alltronics a bit of a plug because I am very happy with their service and the quality of their kits.


If you need a good transformer for the amp - albeit a little small (IMO), Alltronics have the 300VA + 7.5VA toroid on special for $60


Also; - Last week they had the ULD MK2 135Watter on special for $59 ea. I have performed the MK3 upgrade on that one and this has saved me $30 per board.


This is not a paid commercial, like those silly ads that come onto your tv at 3am in the morning, but a heartfelt plea for Aussies to support the locals. We need these people to stock the goodies or we will have to buy all our components from China. This is not a bad thing I reckon, but it takes ages for your gear to arrive.


If you are considering building the ULD in any form, and you live in Oz then keep an eye on the Alltronics site because they are a teriffic mob and I can assure you that their boards are of superior design and quality to the Chinese ones that I have brought time and again, only to find that I have been left up the creek without a paddle, when I find NO INSTRUCTIONS or even a SCHEMATIC!

Quote Me:- If Forestry Tasmania and the Tas Govt continue to trample swathes of scrub here, we will have no timber to build speakers and the Army will have to change it's uniform 'cause their camoflage will contrast with the naked red dirt of the wastelands.


Cheers - Phil
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Old 1st February 2012, 02:23 AM   #30
farmerjack61 is offline farmerjack61  Australia
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Quote:
Originally Posted by Oliphant View Post
Thanks jcx. I might just try this with my next design and measure the difference between large and small input caps. I've recently recieved his latest edition of the power amplifier design handbook and I'll make sure to look this up
Hi there Ollie' My name is Phil and I just wanted to ask if that book is a good reference? I have another book; "Self on Audio Second Edition" it is a teriffic source of info. Sometimes I feel that you have to read this info two or three times before you actually adopt some of his methods and incorporate them into your designs.

His name keeps popping up on these sites because I think he explains things pretty well. When I look at Silicon Chip's ULD 135 Watter, in schematic form I see the speaker protection module is a reasonable copy of self's DC protection circuit, but Silicon chip has added and tweeked it to suit our requirements, so I'm not complaining.

I would have built a Blameless from Self's site (the site referenced in the aforementioned book) knowing that It would be spot on and just what the doctor ordered, but I'm afraid they are a little out of my price range.

Cheers
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